1. Field of the Invention
The invention concerns a photonic switching matrix for implementing a multistage switching network. It provides for point-to-point and point-to-multipoint connections for switching data in the form of fixed length cells asynchronously time-division multiplexed onto optical fibers.
2. Description of the prior art
The article: ATM photonic switching network, reference 14B2 of TOPICAL MEETING ON PHOTONIC SWITCHING, KOBE, JAPAN, Apr. 12-14, 1990 describes a photonic switching matrix comprising:
an input interface module at each of the n inputs of the matrix for identifying the cells arriving at said input by reading a virtual channel label or virtual circuit group label included in the header of the cell and to convert the wavelength of each cell into a wavelength representing one output of the matrix; PA1 cell selectors each comprising a splitter and filters for distributing the cells to the outputs of the matrix according to their wavelengths; and PA1 an optical buffer for each output for storing cells addressed to the same output and which may be in conflict for access to that output. PA1 n optical memories having a capacity equal to one cell and which can be in the form of an optical delay line; and PA1 an n.times.m spectral division switch. PA1 a plurality of wavelength converters at respective inputs of the matrix to assign a wavelength to each cell applied to an input of the matrix; PA1 an optical buffer common to all the outputs of the matrix for storing each cell for a duration selectable between 0 and k.T.sub.c where k is an integer and T.sub.c is the duration of a cell; PA1 a space routing stage comprising a filter for each output of the matrix passing to a given output only cells having a given wavelength; and PA1 control means for controlling the converters and the buffer according to routing information indicating for each cell the output of the matrix to which said cell is addressed and for selecting the duration for which each cell is stored in the buffer so as to construct a queue for each output to avoid conflicts between two cells to be switched to the same output; PA1 (k+1) delay lines respectively introducing time-delays 0, . . . , k.T.sub.c and having outputs connected to inputs of the space routing stage; PA1 (k+1) combiners each having an output connected to an input of a delay line and n inputs; PA1 n splitters each having an input constituting an input of the buffer and (k+1) outputs; and PA1 (k+1).n optical gates each connecting an output of one of the n splitters to an input of one of the (k+1) combiners and controlled by the control means so that each splitter is connected to a single combiner at a time.
A disadvantage of this known type of switching matrix is that it requires an optical buffer for each matrix output. Each of these buffers comprises:
This n.times.m switch comprises wavelength converters for converting the wavelength of each cell, cell by cell, a combiner, a splitter and filters which can be tuned to route each cell into one of the optical memories. The optical memories being connected in series, they provide for introducing a time-delay between 0 and m times the duration of a cell.
A disadvantage of this known type matrix is that it requires a buffer for each matrix output which increases the number of components and therefore the manufacturing cost.
An object of the invention is to propose a simpler photonic switching matrix that is less costly than this known type matrix but which enables a multistage switching network to be implemented by combining a plurality of matrices in accordance with the invention and which caters for both point-to-multipoint connections and point-to-point connections.